1. Field of the Invention
The invention concerns the manufacture of smart cards capable of operating with or without contact. These cards are provided with an antenna integrated in the card and a micromodule connected to the antenna. Information is exchanged with the exterior either by the antenna (therefore without contact) or by contacts flush with the surface of the card.
Throughout the rest of the description this type of card will be called a mixed card or mixed smart card.
The manufacturing method also concerns contactless smart cards, that is smart cards capable of operating without contact, information being exchanged with the exterior only through the antenna.
However, to simplify the following explanation only mixed cards will be referred to in what follows, although the method also extends to contactless smart cards, as has just been stated.
2. Related Background
Mixed smart cards are intended to facilitate various operations, such as banking operations, telephonic communications, identification operations, operations for discharging or recharging units for account, and all kinds of operations which can be carried out either by inserting the card in a reader or remotely by electromagnetic coupling (in principle of the inductive type) between an emitter-receiver terminal and a card placed within the field of action of this terminal.
Mixed cards must have standardised dimensions identical to those of conventional smart cards fitted with contacts. This is also desirable for cards operating only without contact.
It will be recalled that cards with contact are defined by the usual standard ISO 7810, this definition being: a card which is 85 mm long, 54 mm wide and 0.76 mm thick. The flush contacts are at clearly defined positions on the surface of the card.
These standards impose severe constraints on manufacture. In particular, the very low thickness of the card (800 μm) is a major constraint, still more severe for mixed cards than for cards simply fitted with contacts, as incorporation of an antenna in the card must be provided for.
The technical problems which are posed are problems of positioning the antenna in relation to the card, as the antenna occupies almost the whole surface of the card, problems of positioning the integrated circuit module (comprising the microchip and its contacts) which makes possible the electronic operation of the card, and problems of the precision and reliability of the connection between the module and the antenna; finally, constraints of mechanical strength, reliability and manufacturing cost have to be taken into account.
The antenna is generally formed by a conductive element deposited as a thin layer on a plastic support sheet. At the ends of the antenna connecting pads are provided; these must be exposed in order to be able to connect with the contacts of the electronic module.
In the following description the conductive element forming the antenna will be called the antenna filament, given that, depending on the technology used, it may comprise a filament inlaid in the support sheet or printed tracks.
One approved solution for manufacturing mixed smart cards consists in using plastic foils pre-perforated in the area of the connecting pads of the antenna formed by the two ends of the antenna filament, in superimposing them on the sheet supporting the antenna and in assembling them by hot or cold lamination. The position of the connection pads of the antenna is limited by the position of the electronic module which is itself defined by the ISO standards.
A cavity to accommodate the electronic module must then be machined in the body of the card, between the connection pads of the antenna and above the perforations formed in the plastic foils covering the antenna; then the contacts of the electronic module must be connected to the connection pads of the antenna by depositing a conductive adhesive in the perforations. The antenna filament generally comprises several turns. These turns pass between the connection pads in such a way that they can be connected to these pads, which are located near the micromodule.
A first problem then arises from the nature of this structure. The turns may be damaged when the cavity is machined. Indeed, the turns can even be destroyed during this stage if the antenna is not positioned very precisely in relation to the position of the cavity.